A number of automobiles now provide wipers for rear windows where the rear window has a tendency to become deposited with contaminants and rain water that obscure the rear field of vision. These wipers are in many respects similar to conventional front windshield wiper systems in operation.
More specifically, a conventional window wiper system typically has at least one pivotal wiper arm fitted with a rubber blade to effect a squeegee action when the wiper arm is pivoted through a wipe pattern across the window. The wiper arm begins at rest from a park position on the edge of the glass boundary of the window and initially traverses a park stroke to enter a reciprocating, pivotal motion through the wipe pattern. The wiper concludes its operation by traversing the park stroke in the opposite direction and returning to the park position. This sequence of motion is governed by a wiper motor and transmission which are conventional in the art.
It is often desirable to remove the wiper blade from the glass pane of the window during the park stroke. It is necessary to remove the wiper blade from the glass pane when the vehicle window is of the drop glass type, i.e. where the glass may be retracted within the body or door panel of the vehicle to open the window and may be extended into the window opening to close the window. This type of window must be fitted with a wiper which parks off the glass to permit window opening and closing.
The air and liquid seal or molding which is generally provided between the window glass and frame to provide a seal between the two requires that the window glass must be recessed relative to the frame. As a consequence, any wiper fitted to such a window must be capable of movement with two degrees of freedom, i.e. through the dimension of recess and through the wipe pattern on the glass surface.
It is known to provide an inclined surface or a cam face which operates with the arm of a windshield wiper mechanism in such a manner that when the arm and thereby a blade thereof moves to a rest or park position the blade is lifted off the windshield to free it of stress. However, in many instances space limitations make it difficult to provide such an inclined cam face, or else require that the cam face be at a location on the vehicle which presents unacceptable problems either from a point of view of aesthetics or for operational considerations. For instance, the location must be such that the windshield wiper arm does not freeze to the cam face in cold weather conditions.
Prior patents disclose windshield wiper mechanisms which include cams which guide the wiper arms from a working position where the wiper blade contacts a window pane to a rest or park position where the wiper blade is moved away from the surface of the window pane and is disposed in an out-of-the-way position relative to the window. For example, the U.S. Pat. No. of Dunhill et al, 4,091,494 discloses an adjustable mounting with a pair of threaded fasteners having a guide or cam which projects outwardly from the pane of the glass. The cam functions like a ramp to guide the wiper blades through the park stroke. Likewise, the U.S. Pat. No. of Mainka 3,604,048 discloses a wiper system including guide means in the form of a cooperating cam and follower to impart axial movement to the wiper arm to lift it off the windshield in a rest position.
Other wiper mechanisms generally of the type to which this invention relates are disclosed by the U.S. Pat. Nos. of Hatch, 3,019,468, Carpenter et al, 3,107,383, Burke, 1,787,894, Oishei, 1,826,672, Oishei, 1,937,160, Dangler, 3,110,920, and O'Steen, 4,040,141.